1. Field of the Invention
This invention relates to a process for the manufacture of quinophthalone dyes, in particular Solvent Yellow 33, also known as D & C Yellow 11. In one aspect, the invention relates to the manufacture of Solvent Yellow 33 by condensation of quinaldine with excess phthalic anhydride which is employed both as a solvent and as a reactant. In another aspect, the invention relates to the manufacture of Solvent Yellow 33 by condensation of quinaldine with excess phthalic acid in which the acid is used both as a solvent and as a reactant. In yet another aspect, the invention relates to the use of both phthalic anhydride and phthalic acid, one as a reactant and the other as a solvent for the reaction. In still another aspect, the invention relates to the use of recycled phthalic acid as a solvent for the reaction.
2. Description of the Prior Art
The classical method for manufacturing dyes is described in British Patent No. 1362 issued to Denton. Denton teaches a process which involves the condensation of pyridine or chinoline bases with phthalic anhydride in the presence of zinc chloride.
Improvements to this method have occurred since Denton. Today, the conventional process for the manufacture of quinoline yellow dyes is to react a quinaldine derivative with phthalic anhydride in the presence of an inert organic liquid employed as either a solvent or as a diluent (see U.S. Pat. No. 1,963,374 to Ogilvie). For example, Ort, et al. teaches in U.S. Pat. No. 5,106,980 a process for the preparation of a quinophthalone by condensing 8-aminoquinaldine with a phthalic anhydride in the presence of molten benzoic acid acting as diluent and promoter.
Other prior art references disclose methods of manufacturing quinoline yellow dyes, such as 2-(2-quinoyl-6-sulfonic acid)-1,3-indandione (also known as D & C Yellow 10) and 2-(2-quinoyl-6-sulfonic acid)-1,3-indandione-5-sulfonic acid (also known as E 104). These water soluble dyes can be manufactured either by a two-step process which involves a condensation reaction and then the sulfonation of the quinophthalone or a one step process which involves the condensation of a sulfonated intermediate. Clarke, for example, teaches the one step process in U.S. Pat. No. 3,108,109. Specifically, he teaches that quinaldine sulfonic acid can be condensed with phthalic anhydride in the presence of a reaction promoter selected from the group consisting of dimethylacetamide, dimethylformamide and mixtures of the said amide reaction promoters. Sulfonated intermediates, however, cannot be used in the direct manufacture of Solvent Yellow 33.